1. Field of the Invention
This invention relates to a lighting device provided with a lighting instrument with an incandescent lamp which is applied as a light source, and more particularly a dimmer for an incandescent lamp which is suitable for use in stage lighting or TV studio lighting.
2. Description of the Related Art
Although many lighting devices are used in the field of stage lighting or TV studio lighting and the like, a free adjustment of light for a light flux in the lighting equipment is an essential element and a smooth optical adjustment can be carried out, so that also at present, the lighting instrument with an incandescent lamp such as a halogen lamp which is applied as a light source is frequently used.
Optical adjustment of this incandescent lamp lighting device is carried out by controlling a phase angle of an electrical power supplied to the lighting instrument under application of a switching element such as a thyrister and the like.
However, it is well known in the art that when a voltage supplied to the incandescent lamp lighting equipment is controlled to perform an optical adjustment, a color temperature of the light flux generated by the incandescent bulb is substantially varied.
In particular, in the case of TV studio lighting using TV cameras, a variation in color temperature caused by optical adjustment may provide a substantial influence against image quality of TV screen image and this may provide a certain problem so that in order to solve this problem in the prior art, there have been provided some measures that a color filter is used at the lighting equipment to correct a color temperature, or in place of optical adjustment a radiating range angle of the lighting equipment is changed to adjust an illuminance at a lighted surface.
In general, it has been required that a light flux of the halogen lamp is proportional to a multiplication by 3.38 of a supplied voltage and a color temperature is proportional to a multiplication by 0.36 of a supplied voltage in reference to an experiment. Accordingly, a color temperature is proportional to a multiplication by 0.107 of a light flux.
For example, in the case that the halogen lamp with 3,200K at a rated voltage is used, optical adjustment of the light flux is performed to 50%, the color temperature is reduced down to 2,970K. FIG. 1 is a graph showing a specific light flux against a color temperature in the prior art incandescent lighting equipment.
In regard to a less amount of variation in color temperature, although the prior art employed a system in which the reduction in color temperature is avoided by a correction measure with the color filter or adjustment of the lighting equipment as described above, both of them were troublesome measures and they were not necessarily a perfect measures.
In turn, in the gazette of Japanese Patent Publication No. Hei 8-1832 is proposed an optical adjustment method in which when a dimmer circuit is operated in a range of intensity of illumination between 0% and 50% of brightness, only one of a pair of silicon controlling rectifiers is turned on for a predetermined time period and the other silicon controlling rectifier is turned on from a starting point of xc2xd of an entire cycle to its end, and when the dimmer circuit is operated in a range of intensity of illuminance between 50% and 100% of brightness, the other silicon controlling rectifier circuit is turned on against a predetermined portion of the other half cycle, thereby a predetermined pulse duration period for controlling the intensity of illumination given by the lighting device is controlled, this proposal restricts an acoustic noise produced by the lighting device and the reduction in color temperature is not accommodated.
The present invention has been invented in reference to such circumstances as found in the prior art, and it is a first object of the present invention to provide a dimmer for an incandescent lamp in which the color temperature is raised fast even if the optical adjustment is carried out and the optical adjustment can be carried out with a less variation in color temperature.
In addition, it is a second object of the present invention to provide a dimmer for an incandescent lamp capable of adjusting light scarcely acknowledging a reduction in color temperature in which when a degree of adjustment of light is increased, the color temperature is maintained after the color temperature reaches the specified value.
In order to accomplish the aforesaid first object, the present invention provides a gist that a dimmer for performing one ignition for every one period of a power supply waveform is used, each of an electrical power of a positive half cycle and an electrical power of a negative half cycle is supplied to each of individual filaments of the bulb, a time of raising of the adjusted light at each of the filaments is displaced and a variation of the color temperature caused by the optical adjustment operation is reduced.
That is, a first aspect of the present invention consists in a dimmer for an incandescent lamp capable of adjusting light with a less variation in color temperature in which a phase angle controlling optical adjuster for performing one ignition operation every one period of the electrical power waveform is used and its ignition angle is changed continuously to perform an optical adjustment operation, each of the electrical power of positive half cycle and the electrical power of negative half cycle is supplied to each of the individual filaments.
In accordance with such means as described above, the electrical power of positive half cycle and the electrical power of negative half cycle are controlled continuously for optical adjustment, each of the electrical powers is supplied to individual filaments to cause one filament to be raised fast and the other filament to be raised in delay, resulting in that a variation in color temperature can be reduced remarkably when the optical adjustment is performed.
As an embodiment of the individual filaments in the aforesaid first aspect, it is possible to provide an embodiment in which the bulb having two filaments enclosed with an intermediate terminal installed in the same bulb is used.
In addition, a rated electrical power ratio of the two filaments enclosed in the aforesaid same bulb is changed to enable the characteristic in variation of color temperature to be optionally set.
As an embodiment of the individual filaments in the aforesaid first aspect, a plurality of bulbs are installed within the same lighting equipment, one bulb lit in optical adjustment in a positive half cycle and the other bulb lit in optical adjustment in a negative half cycle are discriminated to enable a similar effect to be attained. A plurality of bulbs defined in this case are two bulbs or more and they include both an even number and an odd number.
It is preferable that a rated electrical power ratio of a plurality of bulbs installed in the aforesaid same lighting equipment is changed.
As an embodiment of means for continuously changing an ignition angle of the phase angle controlling optical adjuster related to the aforesaid first aspect, it can be accomplished by arranging the optical adjustment controlling function signal generator forming the waveform synchronized with the power supply waveform and corresponded to one period of the power supply, a comparator and a switching element.
In order to accomplish the aforesaid second object, the present invention has a gist in which a dimmer capable of individually controlling the electrical power of positive half cycle and the electrical power of negative half cycle is used, each of the electrical power of positive half cycle and the electrical power of negative half cycle is supplied to each of the individual filaments of the bulbs, supplying of the electrical power in the second filament is started when the first filament while increasing the specific light flux reaches a specified color temperature (for example, 97% of the rated color temperature), at this time a reduction in color temperature caused by lighting up of the second filament is accommodated by further increasing a supplying of the electrical power at the first filament, thereby a reduction in the color temperature caused by starting the lighting up the second filament is prevented.
That is, the second aspect of the present invention is characterized in that there is provided a dimmer capable of individually controlling a positive half cycle and a negative half cycle of an AC power supply voltage, the electrical power of the positive half cycle and the electrical power of negative half cycle are discriminated by the dimmer and each of the electrical powers is supplied to another filament of the bulb, and at the same time, when the first filament reaches the specified color temperature, supplying of the electrical power to the second filament is started, supplying of the electrical power to the first filament is further increased to accommodate for a reduction in the color temperature.
In accordance with the second aspect of the present invention, it is possible to eliminate the improvement left by the aforesaid first aspect and to prevent a reduction in color temperature during the adjustment of light.
More particularly, in the aforesaid first aspect, the second filament starts to light up after the first filament in the bulb reaches the rated electrical power (100% of a rated color temperature) when the specific light flux rises continuously as shown in FIG. 2, so that it is acknowledged that a slight reduction in color temperature occurs during a time in which the second filament reaches the rated electrical power. The second aspect of the present invention improves this feature, resulting in that an optical adjustment with a quite less variation of color temperature in the incandescent lamp lighting equipment can be carried out.
As an embodiment of another filament in the bulb in the aforesaid second aspect, similar effect may also be attained by applying a bulb enclosed with two filaments having an intermediate terminal in the same bulb, and by separately supplying an electrical power of the positive half cycle and an electrical power of the negative half cycle to each of the filaments in the bulb.
In addition, a characteristic in variation of color temperature can be optionally set by relatively changing the rated electrical power ratio of the two filaments enclosed in the aforesaid same bulb.
As an embodiment of another filament in the bulb in the aforesaid second aspect, a plurality of bulbs can be installed in the same lighting equipment and the bulbs optically adjusted to be lit can be discriminated with the electrical power of positive half cycle and the electrical power of negative half cycle. In this case, a plurality of bulbs are defined as two or more bulbs and any of the even number of or odd number of bulbs can be included.
Further, the rated electrical power ratio of a plurality of bulbs to be installed in the aforesaid same lighting equipment are relatively changed, resulting in that a characteristic of the variation in the color temperature can be optionally set.
As an embodiment of the dimmer relating to the aforesaid second aspect, it can be accomplished by using a dimmer comprised of an optical adjustment control function signal generator synchronizing with an electrical power waveform and formed with a waveform corresponding to one period of the electrical power, a comparator, and a switching element for controlling respectively each of the electrical power of the positive half cycle and the electrical power of the negative half cycle, wherein it is formed such that a function waveform of the aforesaid function signal generator and an output of an operating unit for performing an optical adjusting operation are compared by the comparator, an output can be attained at the comparator for a period in which an output of the operating unit exceeds a voltage of the function waveform, the switching element is ignited with the output of the comparator, an ignition angle of the phase angle controlling dimmer is changed continuously, each of the electrical power of positive half cycle and the electrical power of negative half cycle is supplied to a separate filament and at the same time when the first filament reaches a specified color temperature, supplying of the electrical power to the second filament is started and supplying of the electrical power to the first filament is further controlled to be increased.
As the aforesaid optical adjustment control function signal generator, it can be applied whatever devices of the analogue device and the digital device may be applied.